Research On Variable Flow Water Control Strategy Of Air-source Heat Pump Heating System In Cold Region

With the implementation of the “heating on demand” concept,the user's terminal heating equipment is equipped with a thermostat to adjust the heat supply.The terminal regulation leads to variable flow on the transmission and distribution side,therefore,the primary pump variable flow system with the air source heat pump unit as the heat source is gradually applied.However,in the actual application process,there is a lack of theoretical research on the variable flow system of the air source heat pump.This paper studies the variable flow control strategy of the air source heat pump heating system in cold regions through theoretical analysis and simulation.This paper firstly conducts a theoretical analysis of the variable flow system of the air source heat pump,which involves the system type and working principle of the variable flow system of the air source heat pump,the variable speed adjustment control method of the pump and the corresponding terminal flow adjustment method,the differential pressure bypass control method,the effect of different terminal flow adjustment methods on the supply and return water parameters of the air source heat pump unit and the overall hydraulic balance of the variable flow system of the air source heat pump.In the differential pressure bypass control method,the bypass branch uses a combination of a solenoid valve and a differential pressure bypass valve,which can ensure the minimum allowable flow of the heat pump unit.In order to study the effect of variable flow on the performance of the heat pump unit,this paper established a simulation model of the variable frequency air source heat pump unit.In the shell-and-tube condenser simulation model,temperature difference control variable flow simulation model,pressure difference control variable flow simulation model and constant flow simulation model were established to study the effect of variable temperature control variable flow and differential pressure control variable flow on the performance of variable frequency air source heat pump unit,the constant flow simulation model is a comparative model.Considering the influence of the change of the number of heat pump units on the control curve of the water pump,this paper establishes the pipe network model of the variable flow system of the air source heat pump,and studies the variable speed regulation control strategy of parallel pumps based on differential pressure control and temperature difference control,and give the differential pressure bypass design method of different parallel pumps variable speed regulation control strategies.At the same time,the pump performance and energy saving effect of different parallel pumps variable speed adjustment control strategies are compared and analyzed.In order to study the control strategy of heating terminal regulation,this paper builds a mathematical model of floor radiant heating room based on automatic control theory,and establishes a simulation model of floor radiant heating system.The terminal adjustment control strategy based on temperature difference control and pressure difference control is studied,and the control performance of different terminal adjustment control strategies is optimized and analyzed.